The present invention relates to a method of conditioning a particle filter provided for receiving exhaust gases from an internal combustion engine.
The invention also relates to an internal combustion engine system, comprising at least one combustion chamber, in which internal combustion takes place, an exhaust gas system connected to said combustion chamber, a particle filter arranged in said exhaust gas system, and a control unit provided with software for controlling at least one combustion control parameter that affects the characteristics of particles emitted together with and carried by exhaust gas from the combustion chamber to the exhaust gas system.
Diesel engines of today are normally equipped with a diesel particle filter arranged in the exhaust gas system connected to the engine. A diesel particulate filter (or DPF) is a device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine. Wall-flow diesel particulate filters usually remove 85% or more of the soot, and under certain conditions they can attain soot removal efficiencies of close to 100%. Some filters are single-use, intended for disposal and replacement once full of accumulated soot, ash or other particulate matter. Others are designed to burn off the accumulated particulate either passively through the use of a catalyst or by active means such as a fuel burner which heats the filter to soot combustion temperatures; engine programming to run when the filter is full in a manner that elevates exhaust temperature or produces high amounts of NOx to oxidize the accumulated soot or through other methods. This is known as “filter regeneration”. Cleaning is also required as part of periodic maintenance and it must be done carefully to avoid damaging the filter. Failure of fuel injectors or turbochargers resulting in contamination of the filter with raw diesel or engine oil can also necessitate cleaning.
Diesel engines during combustion of the fuel/air mix produce a variety of particles generically classified as diesel particulate matter due to incomplete combustion. The composition of the particles varies widely dependent upon engine type, age, and the emissions specification that the engine was designed to meet. Two-stroke diesel engines produce more particulate per unit of power than do four-stroke diesel engines, as they burn the fuel-air mix less completely. While no jurisdiction has explicitly made filters mandatory, the increasingly stringent emissions regulations that engine manufactures must meet mean that eventually all on-road diesel engines will be fitted with them. In the European Union, filters are expected to be necessary to meet Euro VI heavy truck engine emissions regulations and future requirements on the number of emitted particles presently discussed.
There are a variety of diesel particulate filter technologies on the market. The most common filter is made of cordierite a ceramic material that is also used as catalytic converter supports (cores)). Cordierite filters provide excellent filtration efficiency, are (relatively) inexpensive, and have thermal properties that make packaging them for installation in the vehicle simple. The major drawback is that cordierite has a relatively low melting point (about 1200° C.) and cordierite substrates have been known to melt down during filter regeneration. The second most popular filter material is silicon carbide, SiC. It has a higher (2700° C.) melting point than cordierite. However it is not as stable thermally. Fibrous ceramic filters are made from several different types of ceramic fibers that are mixed together to form a porous media. This media can be formed into almost any shape and can be customized to suit various applications. Some cores are made from metal fibers—generally the fibers are “woven” into a monolith. Such cores have the advantage that an electrical current can be passed through the monolith to heat the core for regeneration purposes. There are also disposable paper cores that are used in certain specialty applications, however without a regeneration strategy. The different types of filters can be divided into coated filters (being coated with a reactive agent thereon) and non-coated filters.
Regeneration is the process of removing the accumulated soot from the filter. This is done either passively (from the engine's exhaust heat in normal operation or by adding a catalyst to the filter) or actively introducing very high heat into the exhaust system. On-board active filter management can use a variety of strategies:
1. Engine management to increase exhaust temperature through late fuel injection or injection during the exhaust stroke
2. Use of a fuel borne catalyst to reduce soot burn-out temperature
3. A fuel burner after the turbo to increase the exhaust temperature
4. A catalytic oxidizer to increase the exhaust temperature, with after injection (HC-Doser)
5. Resistive heating coils to increase the exhaust temperature
6. Microwave energy to increase the particulate temperature
All on-board active systems use extra fuel, whether through burning to heat the DPF, or providing extra power to the DPF's electrical system, although the use of a fuel borne catalyst reduces the energy required very significantly. Typically, a computer decides, based on pre-programmed set points, when to activate the regeneration cycle. Set points may be fuel injection history, for example when a predetermined amount of fuel has been consumed since the foregoing regeneration, or when a predetermined time has passed since a foregoing regeneration. The additional fuel can be supplied by a metering pump. Running the cycle too often while keeping the back pressure in the exhaust system low will result in high fuel consumption. Not running the regeneration cycle soon enough increases the risk of engine damage and/or uncontrolled regeneration (thermal runway) and possible DPF failure.
Diesel particulate matter oxidizes at a suitable rate when temperatures above 550 degrees Celsius are attained. This temperature can be reduced to somewhere in the range of 350 to 450 degrees Celsius by use of a fuel borne catalyst. The actual temperature of soot burn-out will depend on the chemistry employed. The start of combustion causes a further increase in temperature. In some cases, in the absence of a fuel borne catalyst, the combustion of the particulate matter can raise temperatures above the structural integrity threshold of the filter material, which can cause catastrophic failure of the substrate. Various strategies have been developed to limit this possibility. Note that unlike a spark-ignited engine, which typically has less than 0.5% oxygen in the exhaust gas stream before the emission control device(s), diesel engines have a very high ratio of oxygen available. While the amount of available oxygen makes fast regeneration of a filter possible, it also contributes to runaway regeneration problems.
Some applications use off-board regeneration. Off-board regeneration requires operator intervention (i.e. the machine is either plugged into a wall/floor mounted regeneration station, or the filter is removed from the machine and placed in the regeneration station). Off-board regeneration is not suitable for on-road vehicles, except in situations where the vehicles are parked in a central depot when not in use. Off-board regeneration is mainly used in industrial and mining applications. Coal mines (with the attendant explosion risk from coal damp) use off-board regeneration if non-disposable filters are installed, with the regeneration stations sited in an area where non-permissible machinery is allowed. Many forklifts may also use off-board regeneration—typically mining machinery and other machinery that spend their operational lives in one location, which makes having a stationary regeneration station practical. In situations where the filter is physically removed from the machine for regeneration there is also the advantage of being able to inspect the filter core on a daily basis (DPF cores for non-road applications are typically sized to be usable for one shift—so regeneration is a daily occurrence).
An inherent characteristic, and drawback, of the diesel particulate filters now on the market is that, in their empty state, i.e. when they are new or when then they have just been regenerated to a certain degree, their capability of trapping small particles, in the nanometer range, is reduced in comparison to when they are in a more filled-up state. Since recent research points in the direction that such small particles, even though they may be only a small fraction of the total weight of particles emitted from the engine, are probably more dangerous to the environment and to living beings than previously expected, this drawback of contemporary filters should be taken into consideration during the design of models of when and how to regenerate diesel particle filters.
The regeneration of a diesel filter may either be partial or full, wherein full regeneration is here referred to as when the weight of remaining particles in the regenerated filter is less or equal to 10% of the maximum weight of particles that can be trapped in said filter. Full regeneration has the advantage of being relatively easy to achieve and that is relatively uncomplicated to establish the conditions for how to achieve it. However, until the filter has been partly refilled after such a full regeneration, the ability thereof to trap smaller particles, within and below the nanometer range, will be reduced, thereby leading to an increased emission of such particles in connection to the regeneration of the filter.
Partial regeneration, on the other hand, is a way of remedying the above-mentioned drawback since the unwanted empty state of the filter is thereby avoided. Partial regeneration is based on the principle that a computer associated to the engine makes a prediction of the filling degree of the filter on basis of the foregoing operation data of the engine. When the filling degree is predicted to be at a certain level (preferably for), regeneration is initiated. However, the regeneration is not completed such that the filter is emptied. Instead the computer is programmed to make a further prediction of the filling degree of the fitter based on the regeneration data and to stop the regeneration when the filling degree is predicted to be at a certain level. This kind of control of the filling degree of the filter has proven to be fairly suitable for non-coated filters. However, for coated filters partial regeneration it is not equally suitable since, on one hand, the latter need to be fully regenerated in order to maintain their best possible functionality, and, on the other hand, the filling degree of such filters is more difficult to establish based on previous operation data of the engine, and that, therefore, after some time the computer will not be able to correctly predict the right filling degree and when to initiate the regeneration.
A method is provided for conditioning a particle filter provided, for receiving exhaust gases from an internal combustion engine, wherein said method comprises the steps of providing a first engine control mode and a second engine control mode, wherein in the second engine control mode at least one combustion control parameter that affects the characteristics of particles emitted together with and carried by the exhaust gases from the engine is different in relation to the first control mode such that the filling rate of the particle filter with particles that will increase the ability of the particle filter to entrap smaller particles is increased compared to the filling rate that would have been achieved with the first engine control mode, and temporarily applying said second engine control mode to the engine as a response to a regeneration of the particle filter or based on a current soot loading status.
Optionally, the method includes also the step of determining said current soot loading status.
Optionally, the second engine control mode is selected as a response to a performed regeneration or comparison of said current soot loading status with a predetermined soot loading status, e.g. when it is established that a predetermined level of soot load, in the filter has been reached.
Regarding the term “regeneration”; the second control mode is applied after regeneration has been performed (actively) or has occurred (passively).
The soot loading status may be referred to as the mass of particulate matter trapped in the particle filter. Alternatively the soot loading, status may be referred to as the efficiency of the filter to entrap particles, in particular the ability of thereof to entrap smaller particles as defined later, which in turn s dependent on the mass of particulate matter entrapped in the filter and the constitution of such particular matter.
The particles the filling rate of which is increased have such physical properties (size, shape and surface properties) that they will be trapped by the filter. Smaller particles have a tendency to adhere to such particles, whereby small particles that would otherwise have passed through the filter will get entrapped by the latter. In other words, the second control mode is such that there will be an increased emission of said particles from a combustion chamber of the engine from which exhaust gases are conducted to the particle filter.
Optionally, a determined low level of the soot loading status initiates applying said second engine control mode to the engine. Accordingly, the second control mode is applied when it is determined that the soot loading in the filter is below a predetermined threshold value.
Optionally, the determined low level of the soot loading status is represented by regenerated particulate filter.
Optionally, the method comprises performing a regeneration of the diesel particle filter.
Optionally said method comprises, before said regeneration applying said first control mode. Preferably, the first control mode is a mode which is different from the control mode applied during the regeneration.
Optionally, said soot loading status is determined by an estimated soot load. In other words, in particular when there is no active regeneration performed, and the filter is assumed to reach a predetermined lower level of soot load as a consequence of the mere operation conditions without any such active performing of regeneration, the trigging, of the application of the second control mode may be based on an estimation of the soot load. The estimation may be based on hours of operation or other operation data of the engine, such as fuel injection history, fuel consumption, etc.
Optionally, said soot loading status is determined by an estimated soot trapping efficiency. In cases in which it is possible to measure or estimate the soot trapping efficiency of the filter, in particular the efficiency thereof of trapping small particles as defined herein, the application of the second control mode may thus be triggered when the estimated or measured particle-trapping efficiency of the filter is below a predetermined threshold value.
Optionally, the second engine control mode is a mode that is applied as a response to a passive or active regeneration of the filter having been performed or occurred. Preferably, the first engine control mode is a major control mode that is applied during most part of the total time of operation of the engine and designed for low emission of particles, i.e. low total mass of soot particles emitted from a combustion chamber of the engine and conducted through an exhaust gas system to the particle filter. The first control mode must not be applied immediate before the regeneration, but according to one example it is. The first engine control mode may include more than one major control mode and may also include transient modes that are applied between further major modes. The first engine control mode thus results in a mean control of said parameter (represented by the contributions of the possible major and transient modes that form part of said first control mode). The second engine control mode alters the control of said parameter compared to this mean value of the first control mode such that said increased filling rate is achieved. The first (and major) engine control mode, that according to prior art would have been applied directly after and/or during, the regeneration is thus temporarily replaced by the second control mode, which makes the filter speed up the retaining of its ability of trapping smaller particles. Smaller particles may be referred to as particles with a diameter<50 nanometers, preferably particles with a diameter<10 nanometers. By temporarily increasing the rate of filling-up of the filter, less total mass of said smaller particles will pass the filter than if the first control mode would have been applied instead of said second control mode. When the filter has regained a predetermined level of trapping small particles, the second control mode is replaced by the first control mode. For an operation cycle between two consecutive regenerations, the first mode is applied for a longer time than the second mode. Preferably, during such a cycle, the first mode is applied substantially longer than the second mode, preferably more than 100 times longer. It is preferred to use the method on an engine arranged in a vehicle adapted for generally constant operation conditions over longer time, preferably a heavy duty truck adapted for long trips at generally constant engine load. In other words, a major part of the distance traveled by such a vehicle or operation time of the engine is done at generally constant engine load, during which the first operation mode is preferably applied. The first and second engine control modes are not to be confused with the changes of said combustion control parameter that are caused by a load request from a driver or auto-pilot, but are different control modes that will result in different control of said combustion control parameter for a given load request.
Optionally, said at least one combustion control parameter is altered such that the mean an size of said particles is increased compared to if the first control mode would have been applied. In other words, even if said control parameter is altered such that the total mass of particles (per stroke) would be the same or even lower than if the first control mode would have been applied, the filter will still be more rapidly filled since the particles are now comparatively larger and will to a higher degree be trapped by the filter and fill the latter. Preferably, however, said control parameter is altered such that a larger total mass of particles per stroke is emitted from the combustion chamber than if the first control would have been applied. The result is an even faster initial filling of the filter such that the latter will improve its ability of also trapping said smaller particles.
Optionally, said at least one combustion control parameter is altered such that the weight ratio between particles with a diameter above 50 nm and particles with a diameter below 50 nm is increased compared to if the first control mode would have been applied. Accordingly, the mass of larger particles emitter per stroke from the combustion chamber is temporarily increased in relation to the mass of smaller particles emitted per stroke from the combustion chamber compared to if the first combustion control mode would have been applied.
Optionally it is preferred that, subsequently to said temporary change to the second engine control mode, the software is brought to change from said second engine control mode to a normal operation control mode in which the mean size of particles carried by the exhaust gas from the combustion chamber to the exhaust gas system is reduced compared to if the second engine control mode would have been applied. According to one example, said first control mode is the normal operation control mode. The normal operation mode may also be referred to as a major operation mode.
Optionally, the second engine control mode is maintained until a substantially improved efficiency of trapping of particles with a diameter<50 nm, preferably with a diameter<10 nm, in said particle filter is achieved compared to when said particle filter is in its newly regenerated state. This means that the second control mode is maintained for several continual strokes of the engine, preferably so many strokes that a detectable improvement of the ability of the filter to trap smaller particles is achieved.
Optionally, the regeneration of the filter is a regeneration in which the temperature of the exhaust gases arriving at said filter is temporarily increased such that the particles trapped therein are consumed in a thermo chemical process and the weight of remaining particles in the regenerated filter is less or equal to 10% of the maximum weight of particles that can be trapped in said filter, i.e. the maximum instantaneous mass of soot particles that can be held by the accommodated by the filter.
Accordingly, the regeneration according to this example is a “complete” or “full” regeneration of the litter, and not a partial one, and as explained previously the present invention is particularly suitable for such an application. However, according to an alternative example, the regeneration is a partial regeneration, i.e. a regeneration after which the remaining mass of particles in the filter is more than 10% of the maximum mass of particles that can be trapped in said filter, but where the level of filling of the filter is assessed to be insufficiently high for enabling the filter of trapping smaller particles to sufficient degree, for example with regard to limits established by emission legislation. Preferably, the particle filter is a coated filter with reactive agent thereon.
Optionally, the duration t of said temporary change to the second control mode is more than 20 seconds, preferably more than 1 minute, and even more preferably more than 3 minutes, and below 1 hour, preferably below 30 minutes, and even more preferably below 20 minutes. Accordingly the following possible ranges are claimed: 20 seconds<t<1 hour, 20 seconds<t<30 minutes, 20 seconds<t<20 minutes, 1 minute<t<1 hour, 1 minute<t<30 minutes, 1 minute<t<20 minutes, 3 minutes<t<1 hour, 3 minutes<30 minutes, 3 minutes<t<20 minutes. Preferably, the second control mode is applied immediately after completed regeneration of the filter.
Preferably, the change to the second control mode is automatic, and implemented by software of a control unit that controls the operation of the engine. The duration of the application of the second control mode is a balancing on basis of the need of entrapment of said smaller particles, possibly regulated by contemporary or future emission legislation, and the advantages of letting the engine run in accordance with a normal operation mode. As soon as the filter has been filled to such a level that the entrapment of smaller particles is at an acceptable level, there should be a change from the second control mode to a normal operation control mode, since the latter is assumed to be a more optimised operation mode with regard to efficiency of the engine and emission of particles from the combustion chamber thereof.
Optionally, said at least one combustion control parameter is one or more of the following parameters: total fuel amount per stroke, number of fuel injections per stroke, fuel injection timing, fuel injection pressure, exhaust gas recirculation (EGR) rate, gas mass flow, fuel blend in the case of plural fuel operation. The invention includes alteration of any of said parameters alone or in combination with each other. By altering one or more of these parameters (compared to the normal operation control mode), the soot emitted from the combustion chamber can go from small and dry particles with low mass/size of single particles to bigger wet particles and conglomerates of particles with higher mass/larger size, whereby the latter type of emissions will increase the filling rate of the filter. A “wet particle” is referred to as particulate matter with hydrocarbon, HC, bound thereto.
Optionally, said at least one combustion control parameter comprises fuel injection pressure, and said pressure is reduced with at least 25% compared to the injection pressure that would have been applied in accordance with said first control mode. The fuel injection pressure is a very efficient way of affecting the amount of larger-sized particles emitted per stroke from the combustion chamber. Reduction thereof will increase the number of larger particles emitted per stroke from the combustion chamber to the diesel particle filter and will therefore increase the rate with which the latter is filled and thereby improve the ability of the latter to trap said smaller particles.
Optionally, said at least one combustion control parameter comprises fuel injection pressure, and said pressure is reduced with at least 35% compared to the injection pressure that would have been applied in accordance with said first control mode.
Optionally, said at least one combustion control parameter comprises fuel injection pressure, and that said pressure is reduced with at least 50% compared to the injection pressure that would have been applied in accordance with said first control mode.
Optionally, said at least one combustion control parameter comprises injection timing, wherein the start of the injection (for each stroke) is delayed compared to if the first control mode would have been applied. Delay of the start of injection, or delay of the start of the first of a plurality of injections per stroke, will lead to particles that are larger in size due to soot formation from longer carbon chains that are not oxidized-burnt in the combustion changer. Accordingly the emission of such particles from the combustion chamber will increase as a consequence of the delayed start of fuel injection. Preferably, the start is delayed with at least 6 crank degrees compared to if the first control mode would have been applied.
Optionally, said at least one combustion control parameter comprises fuel injection timing, wherein the end of the fuel injection is delayed compared to if the first control mode would have been applied. A similar technical effect as for the delayed start of the injection is thereby achieved. If a plurality of injections are applied for each stroke, the end of one or more of these is delayed such that the requested technical effect is achieved. Preferably, the end of fuel injection is delayed with at least 6 crank degrees compared to if the first control mode would have been applied.
Optionally, said at least one combustion control parameter comprises total fuel amount per stroke, wherein said amount is increased compared to if the first control mode would have been applied. Preferably the Air-to-Fuel-Ratio (AFR) is thereby decreased compared to if the first control mode would have been applied. A decrease in AFR will have as a result the same technical effect as described above for injection timing, and will thereby contribute to the requested increase of the rate of filling of the filter. Increase of fuel consumption per stroke (for a given requested load and compared to if the first control mode would have been applied) is preferably achieved by reduction of the boost pressure, measured as overpressure, preferably by more than 50% and preferably during more than 3 minutes compared to if the first control mode would have been applied. Such reduction is preferably achieved by any of the following measures: Active waste gate control, Inlet Throttle control, adjusting a variable geometry turbocharger, activating a compressor discharge function (pipe with controlled valve between turbo compressor pressure side and the inlet side), activating a backpressure device reducing area in exhaust system, changing inlet or exhaust valves operation (valve timing or lift). Preferably, the fuel consumption increase is at least 5% compared to if the first control mode would have been applied.
Optionally, said at least one combustion control parameter comprises EGR rate, and that said rate is increased compared to if the first control mode would have been applied. In other words, the amount of recalculated exhaust gas introduced into the combustion chamber for each stroke is increased compared to if the first control mode world have been applied. Thereby, an increased amount of larger soot particles will be emitted from the combustion chamber, such that the filter is more rapidly filled to a level at which the filter will able to trap also very small particles.
Preferably, the EGR rate is increased compared to if the first control mode would have been applied such that the content of carbon dioxide in the gas introduced into the combustion chamber is increased with 2-4% (absolute measure) The carbon dioxide content may be monitored by measurement of the oxygen content of the gas in the inlet manifold, which is thus reduced with at least 2%
Optionally, the at least one combustion control parameter comprises gas mass flow, and that the gas mass flow is reduced compared to if the first control mode would have been applied. The gas mass flow can be controlled by control of a turbine waste gate (which is then a part of the claimed engine), by control of an exhaust back pressure device (which is then part of the claimed engine), by using a turbine with variable geometry and controlling said geometry thereof, by using, and controlling the operation of an inlet throttle, by using and controlling the operation of a compressor recirculation valve or variable valve actuators on inlet or exhaust side of the combustion chamber, or any combination of these suggested control measures and devices. Reduction of the gas mass flow will result in a decreased AFR as described above.
Optionally, the internal combustion engine is a diesel internal combustion engine and the particle filter is a diesel particle filter. However, it should be noted that without such a limitation introduced into the independent claims, the present invention is not restricted only to diesel engines and diesel filters. Accordingly, in the widest sense of the present invention, any combination of fuel, internal combustion engine and filter, not only diesel-based, that will result in a corresponding problem as the one to which the present invention presents a solution will be within the claimed scope of protection.
Optionally, diesel and gas, preferably methane, are used as fuel during the operation of the engine, wherein said at least one combustion control parameter comprises the diesel/gas ratio, wherein the diesel/gas ratio is increased compared to if the first control mode would have been applied. This is a preferred example of a plural fuel engine. Typically, such an engine operates with a diesel/ratio (per stroke or as a mean value for a larger number of strokes) such that, according to the first control mode, more than 40% of the energy generated upon combustion refers to the combustion of gas, while according, to the second control mode less than 20% of the energy generated during combustion refers to combustion of gas. According to one example of the second control mode, only diesel is used as fuel, and combustion of gas, which is to take place in accordance with the first control mode, is zero. These aspects of the invention may be of interest for plural fuel engines, typically diesel-gas engines in which the combusted gas results in emission of very small particles that, for the moment being, is not regarded as critical for the environment, but that may be so in the future. Then a rapid filling of the filter after regeneration thereof may be advantageous also for this kind of engine.
Further, the initially defined internal combustion engine system is provided, wherein said software of the control unit comprises a computer program comprising code means for controlling said at least one combustion control parameter in accordance with the above-defined teaching of the method of the invention. In other words, the computer program is designed so as to initiate application of the second control mode after occurrence of regeneration to a certain level. Preferably the computer program is designed so as to receive operation data from the engine and to control initiation and implementation of the regeneration step when a certain degree of filling of the filter has been predicted by said programme on basis of said operation data.
Operation data may include information regarding engine load, rpm, etc. that has an impact on how fast the filter is filled. The computer programme comprises said software for controlling said at least one combustion control parameter that is altered in accordance with the second engine control mode. Optionally, the computer program emits control signals to any component by means of which said combustion control parameter is directly affected, such as valves by means of which injection pressure and/or timing is affected, valves by means of which fuel amount is affected or valves by means of which EGR rate is affected.
The invention also relates to a computer program product comprising program code means stored on a computer readable medium for performing the control of said at least one combustion control parameter in accordance with the above-defined teaching of the method of the invention when said program is run on a computer.
Finally, the invention also relates to a computer system for implementing the above-defined method of the invention, and comprising, a processor operable to run a computer program comprising code means for controlling said at least one combustion control parameter in accordance with the teaching of the method of the invention.
Further futures and advantages will be present in the following detailed description of examples.